Electric resistance



March 7, 1939.

A. K. DE SCHREVEL ELECTRIC RESISTANCE Filed June 26, 1936 INVENTOR ATTORNEY Patented Mar. 7,1939

st rs N 2,149,841 I rate itiESIS'ENGE 1. Claim. (ca. 291-83) It is not easy to provide electric resistances made from .sintered material with readily adhering contacts that do not yield an undesired contact resistance. For this purpose various methods have been proposed, particularly for electric resistanceshaving a negative temperaturecoeilicient and being made from lower oxides of chromium .or-uranium, while pointing out'that sintering together oi metal and carbon leads to.

iii an undesired result due to the formation 0! car- 'Ihe invention has for its object to provide a 'resistancehaving a negative temperature coeifi cient and being made by sinterlng amixture containing silicon or a silicon alloy, preferably a mixtureto he 'sintered in which the content of silicon is greater than the remaining part.

Now, it'has been found that'such electric resistances can he satisfactorily provided with contacts by means of a carbon material, for example graphite, by sinterlng this carbon material and the resistance material together. 3 x

In order that the invention may 'be clearly understood emf readily carried into efl'ect it as now b'eiset out more fully, by way of example with reference to the accompanying drawing;

grs: oi ierrosilicon having a high content of silicon. i'or: example 98%, is reduced to theform oi a powder, bolted and then mixed with 10 so grs. of'clay and 50 mgrs. o! tragacanth, also in the form ota powder, mixed with the addition ot- 'Z c.-c. until'a uniform isobmaterialat the same time.

tained which is pressed into the shape of small rods l; duringthis treatment the rods have simultaneously pressed to them small graphite blocks 2. The rods I! thus provided with graphite contacts tare then driedin air for afew hours 8 and subsequently heated for about minutes at a temperature of 1300510. in areducing gas atmosphere so that the material slnters. The graphite contacts are thus rigidly connected to the silicon-containing resistance material and do it not exhibit a harmiui contact resistance. They may in addition he provided with small rods 8, for eiample oi nickel, for the supply, of current.

' In further explanation we may mention that an excess of silicon in the resistance material ensures that the resistance value is high at or-= dinarytemperatures' but low at the opera temperature so that a negative coemcient of temperature of high value isobtalned.

What I claim is: t m

a The process of adhering contact pieces toa A resistance stripoi the type which is made up of a composition or materials sintered together after the resistance-strip isshaped as desired which process consists in partially embedding 25 into difierent points of the unsintered but iormed p resistance strip, key shaped pieces -oi carbon material and sintering the resistance. material and the key shaped pieces to the resistance a 

